Apparatus for determining percentage oxygen-saturation of blood



April 26, 1955 E. H. WOOD 2,706,927

APPARATUS FOR DETERMINING PERCENTAGE OXYGEN-SATURATION OF BLOOD Filed Aug. 4, 1949 6 Sheets-Sheet l 2 2 NORMAL l SATURATION CUVETTZ INFPA RED I/v! OFF 2 ELEMENT GALVANOMETER FIG, 1

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APPARATUS FOR DETERMINING PERCENTAGE OXYGEN-SATURATION OF BLQOD Filed Aug. 4, 1949 6 Sheets-Sheet 3 Fia. /0

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INFRA RED INVENTOR. I EARL H. W000 ATTORNEYS Aprll 26, 1955 E. H. WOOD 2,706,927

APPARATUS FOR DETERMINING PERCENTAGE OXYGEN-SATURATION OF BLOOD Filed Aug. 4, 1949 6 Sheets-Sheet 4 EARL H W000 Maw 4 H .9 f Wm April 26, 1955 E. H. WOOD APPARATUS FOR DETERMINING PERCENTAGE OXYGEN-SATURATION OF BLOOD 6 Sheets-Sheet 5.

Filed Aug. 4, 1949 E. H. WOOD APPARATUS FOR DETERMINING PERCENTAGE April 26, 1955 0XYGENSATURATION OF BLOOD Filed Aug. 4. 1949 6 Sheets-Sheet 6 EAR Z0 7* hl a cg zu. 57- I25 NORMAL M a4 R6 305 37/ CUVETTE SALINE R9 "3' 7-4 R4 J8- [29 RED cm. 228 G RI U 95 Rm NORMAL AND cuvs'rrs HG /Z SALINE POSITIONS H SATURATION POSITION 30a EAR 11 wVVWV [/74 2 06 308 EAR 3 0 R2 3% I "l R, 'IZJ' 20; 99 HG INFRA RED POSITION INVENTOR. LARA. H l/Vooo ATTORNEYS United States Patent APPARATUS FOR DETERMINING PERCENTAGE OXYGEN-SATURATION OF BLOOD Earl Howard Wood, Rochester, Minn., assignor, by mesne assignments, to Research Corporation, New York, N. Y., a corporation of New York Application August 4, 1949, Serial No. 108,508

13 Claims. (Cl. 88--14) This invention relates to devices for measuring the absolute value of the arterial oxygen saturation in human beings or animals, either in vivo or by measurements taken on whole blood. The instrument is based upon the spectral transmission characteristics of hemoglobin and utilizes novel pick-up units, filtering arrangements and electric circuits.

An instrument has heretofore been devised (United States Patent No. 2,358,992) which, by means of a photoelectric pick-up unit attached to the human ear, there is provided an indication of the percentage of oxygen saturation of the circulating arterial blood. The first description of a device of this character was published by Matthes in 1935, and descriptions of modifications of such devices and improvements were published in 1938 by Matthes, in 1940 by Hartman and associates, and in 1942 by Millikan and Goldie. These various devices have been designated by the terms oxyhemoglobinograph, oximeter, anoxia photometer and oxyhemograph.

The fundamental data on which in vivo photometric determination of blood-oxygen saturated are based were for the most part elucidated and first applied in Germany by Nicolai, by Kramer and by Matthes. Kramers method was based on the fact that oxyhemoglobin transmits visible red light (6200-7700 A.) to a much greater degree than does reduced hemoglobin. Kramer also demonstrated that Beers law of optical absorption may be applied to hemoglobin as it occurs in the unlaked corpuscles of whole blood. Since Kramers instrument utilized only visible red light, it was not compensated for variations in hemoglobin concentration. Matthes utilized registration of light absorption in two separate spectral regions differently absorbed by oxygenated and reduced hemoglobin and was thus able to compensate for the effect of variations in the concentration of total hemoglobin. Visible red light and green light were selected for this purpose.

Matthes, on the basis of his studies of the absorption of red and infra-red light by whole blood of man and various animal species, was the first to utilize an oximeter which was compensated photoelectrically for changes in the blood content of the organ to which it was applied. For this purpose Matthes used two photocells, each connected to a recording galvanometer. One of the photocells, a barrier layer cell covered with a red filter, was responsive to visible red light and the other, a gas-filled phototube covered with an infra-red filter, was sensitive to infra-red light.

The Millikan oximeter is considerably more compact and convenient to use than is the Matthes oximeter. Millikan used an earpiece containing two barrier layer ironselenium photocells, each covered by a specific Wratten gelatin optical filter.

It has been found that, assuming a constant earpiece light source, the amount of light transmitted through the pinna of the ear and the filters to the photo-electric cells is a function of the fixed characteristics of the respective filters, the amount of ear tissue and the amount and state of oxygenation of the blood in the path of the light.

In the Millikan oximeter the amount of ear tissue and blood in the optical path are sought to be corrected by adjusting the instrument to a supposedly known value of saturation (usually assumed at 98 to 100 per cent when the subject is breathing air or 100 per cent oxygen), while the earpiece is in place on the car on which it is used. Changes in the amount of blood in the optical 2,705,927 Patented Apr. 26, 1955 "ice path are then compensated for electrically by bucking the output of the infra-red cell against the output of the red cell. This method is subject to considerable errors, both from the standpoint of the assumption made and also due to electrical variations in the bucking circuit.

The aforementioned known devices have been subject to certain disadvantages. In known oximeters there is a measurement only of changes and not of absolute values of arterial oxygen saturation, since the instrument must be arbitrarily adjusted at the outset of any run to indicate an assumed value of arterial saturation. The device is usually adjusted to indicate an assumedly correct value of saturation, 98% to 100%, when the subject is breathing air or 100% oxygen.

Matthes calibrated his oximeter against oxygen analyses of capillary blood rendered arterial by histamine iontophoresis of the tissue from which it was obtained. In Matthes work there is no data included concerning the variability encountered between chemical and photoelectrically determined values of arterial oxygen saturation. Calibration data for the Millikan oximeter has been collected by several different laboratories and indi cates that a range of variability from Van Slyke analyses (chemical analyses) is usually Within :5% toward the higher range of' saturation and within 18% toward the lower end (50%) of the saturation scale. Other data has shown that the Millikan oximeter showed a systematic error which +4.7:0.4% and that the error for individual earpieces ranged significantly from +2.1:0.6% to as much as- +13.1i1.8% (for ten earpieces tested).

From the foregoing discussion of the accuracy of the oximeter it can be concluded that errors of oximetric measurement may be of several types, (1) errors due to the inherent variability of the method, (2) systematic errors which may be encountered with certain earpieces,

.and (3) errors inherent in the electrical components, 1. e.

photoelectric cells and circuits.

The deviation encountered between oximetric and chemical determinations of changes of arterial oxygen saturation when using the Millikan type instrument has been demonstrated to be between 4 and 5 per cent saturation when the instrument is used on white subjects. This error is inherent in the instrument and method of use and very probably cannot be reduced significantly. The error is considerably increased, however, if the instrument is used on deeply pigmented ears (Negroes). There is also evidence that oximetric measurements are considerably more variable in patients who have polycythemia than in normal white subjects. The systematic errors encountered with the prior oximeters may be of considerably greater magnitude than the inherent variability of the device. These errors are due to the characteristics of individual earpieces and may be avoided only by calibration of each earpiece against chemical analyses, by careful selection of earpiece photocells in regard to their spectral sensitivity and electrical characteristics or by both methods.

The chief disadvantages of prior oximeters aside from the inherent variability of the method and the necessity of individual selection or calibration of earpieces are 1) that the device must be set at a known value of arterial oxygen saturation and cannot, therefore, be used to measure absolute values of percentage saturation of arterial blood with oxygen; (2) that for this reason it cannot be conveniently used on persons who may have arterial hypoxemia; and (3) that the device does not function properly on dark-skinned persons.

It is an object of the present invention to overcome these disadvantages and to provide an instrument which may be used to measure the absolute values of arterial oxygen saturation on a continuous basis from a pick-up attached to the pinna of the human ear and to provide in the same instrument facilities for the accurate and economical determination of oxygen saturation of whole blood. It is a further object of the invention to provide an improved oximeter instrument wherein a greater degree of accuracy is provided than heretofore available.

It is another object of the invention to provide a rugged and convenient instrument that can be used by various persons without special training, and, when so used, to provide readings of absolute values of arterial oxygen saturation of a high order of accuracy.

It is another object of the invention to provide an improved earpiece for oximeters and an improved photoelectric pick-up device for use in determining the oxygen saturation of whole blood.

It is another object of the invention to provide an improved oximeter system and circuits.

Other and further objects of the invention are those inherent in the apparatus herein illustrated, described and claimed.

The invention is illustrated with reference to the drawings wherein corresponding numerals refer to the same parts and wherein Figure 1 is a front elevational view, partly schematic, showing the oximeter control cabinet, the galvanorneter cabinet and an oximeter earpiece and circuit connections;

Figures 2 through 6 show various views of the oximeter earpiece, Figure 2 being a side elevational view partially sectioned along the line 22 of Figure 3 and partially broken away so as to show the interior details of construction; Figure 3 is a front elevational view, taken in the direction of arrows 3-3 of Figure 2; Figure 4 is a transverse sectional view of the photoelectric cell portion of the earpiece, taken along the line and in the direction of arrows 44 of Figure 2; Figure 5 is an isometric view showing the earpiece in place upon the ear of a patient during the taking of a reading; Figure 6 is an electrical wiring diagram of the earpiece from photocell and from light source to the electrical cable of the earpiece plug connector;

Figures 7, 8, 9 and are views of the cuvette photoelectric pick-up, such as is used for photoelectric determination of the oxygen saturation of whole blood; Figure 7 shows at top view of the oximeter whole blood photoelectric analysis cell or cuvette;

Figure 8 is a vertical sectional view, taken along the line and in the direction of arrows 88 of Figure 7 and showing in addition the tubing connection by means of which the whole blood is withdrawn from and returned to the patient;

Figure 9 is a transverse sectional view, taken along the line and in the direction of arrows 9-9 of Figure 8;

Figure 10 is a wiring diagram of the device shown in Figures 7 through 9 showing the connections from the photoelectric cells and from the light sources to the plug connector of the cuvette unit;

Figure 11 is a wiring diagram of the entire instrument illustrating the wiring and circuit components of the control cabinet, the wiring and circuit components of the earpiece (or cuvette, as it is sometimes known) and the wiring and circuit connections of the galvanorneter unit;

Figures 12, 13 and 14 are, respectively, simplified wiring diagrams illustrating the circuits when the switches shown in Figure 11 are set in certain positions for operation of the unit, Figure 12 illustrating the normal and cuvette saline positions; Figure 13 the saturation position; and Figure 14 the infra-red position;

Figure 15 is a front elevational view showing the A, B and C scales of the two element galvanorneter forming a part of the invention.

Referring to the drawings, particularly Figure 1, there is illustrated the apparatus of the present invention which includes an oximeter control cabinet generally designated 10, a sensitive two-element galvanorneter generally designated 11 and an earpiece generally designated 12. The earpiece 12 may be replaced by a cuvette 70, as hereinafter described. A battery, not illustrated, is used as a source of potential for the instrument, the battery leads being shown at 16. The control cabinet 10 is provided with a plurality of multiple electrical connector jacks at 13, 14 and 15 by means of which the batterv (cable 16) and the pick-up unit, which in Figure 1 is illustrated as the earpiece, or the cuvette 70, and the galvanorneter 1.1 are connected. Thus, the two-wire battery conductor 16 is connected by means of a suitable plug receptacle 17 to the connection block 15, the galvanorneter 11 is connected by a suitable six-wire cable 18 through the plug 19 to the receptacle 13, and the pick-up unit, which in Figure 1 is the earpiece generally designated 12, is connected through a six-wire cable 20 and plug connection 9 to the socket 14. The cable 20 is provided with a connector 2123 by means of which the earpiece 12 may be connected to the instruments, or if the earpiece is desired not to be used it may be replaced by the whole blood analysis cuvette 70 shown in Figures 7-10, hereinafter to be described. The connectors 2123 allow for the ready change from the earpiece to the whole blood analyzing cuvette, where desired, without removing cable 20.

The galvanorneter unit generally designated 11 is provided with a double light source, not illustrated, within its interior and two sensitive coils which are arranged to indicate on the screen 24 which has scales suitably applied thereto for indicating the deflection of the coils in response to signal currents. Any standard two-element high sensitive galvanorneter such as Rugicon Box galvanorneter may be used.

Figure 15 shows the scales as used in the present invention. As shown there is a scale reading from 5 to having the letters A and B adjacent the right end thereof. The indicator light spot A of the red galvanometer scale (scale A) is a half circle of light with a vertical hairline shadow at the center thereof adjusted so as to read on the A (red cell) scale for double scale operation as hereinafter explained. The indicator light spot BC is likewise a half circle of light having a central vertical hairline shadow which is adjusted so as to read on not only the B (infra-red cell) scale for both double and single scale operation, but also in the C scale, which reads directly the per cent oxygen saturation of blood when the instrument is used for single scale operation.

The control panel generally designated 26 of the con trol cabinet 10 includes a plurality of switches and resistor controls designated as follows: A main control multiple gang switch designated S1 is used for setting the controls for any one of five operating conditions which are as follows: Oif position; infra-red position (designated Infra-Red); saturation position (designated Saturation); normal condition (designated Normal); and a position designated cuvette-saline. The switch S1 is a gang switch which will be explained in greater detail hereinafter, and is operated by the single control knob designated S1 in Figure 1. The control panel also includes a plurality of variable resistor controls designated R1, R2, R3 and R4. The controls R1 and R2 for correspondingly designated resistors are used in single scale (single galvanorneter indication) operation wherein the photoelectric cells are arranged in bucking relation to yield a single signal impulse. The controls R3 and R4 for corresponding designated resistors R3 and R4 are used in the double scale operation wherein the output of the photoelectric cells is read as separate indications. The control cabinet likewise includes a meter 27 by means of which the voltage across or current flowing in the illuminating lamp or lamps of the earpiece 12 or cuvette 70 may be read with accuracy. The control panel also includes a switch S3 which controls the battery power to the unit and has an on and off position, a switch S2, which controls the use of the device when either the earpiece 12 or the cuvette 70 is used and has two positions, and the switch S4 by means of which the meter 27 may be reconnected for reading either the voltage or the current in the illuminating lamp circuit of the earpiece or the cuvette.

Referring to Figures 2-6, particularly, there is illustrated in detail the earpiece used for the in vivo analysis in accordance with the present invention. The earpiece includes a frame piece generally designated 30 to which a cylindrical housing 31 is attached by means of the screws 32-32. The housing is provided with a cylindrical sleeve 33 which is normally spring pressed in the downward direction, as shown in Figure 2, by means of the internal spring 34. The housing 31 is provided with a through slot at 35 in which a block 36, which is attached to the sleeve 33, is adapted to slide up and down. Into the block 36 there is threaded a screw 37 on which a clamping nut 38 is adapted to operate. the clamping nut 38 being adapted to press on the saddle 39 which reaches across the width of the slot 35 and presses against the housing 31 on the side areas 4tl40. as shown in Figure 3. When the thumb nut 38 is turned down it thus pushes on the clamping saddle 39, forcing it into engagement with the areas 40-40 of the housing 31 and thus clamps the internal sleeve 33 in any position in which it is adjusted. It may be noted that when the clamping nut 38 is released so as to unclamp the saddle 39, the clamping nut serves as a handle by means of which the internal sleeve 33 may readily be adjusted within the limits of movement of the slot 35. At the upper end of the housing 31, as shown in Figures 2-3, there is a receptacle portion 42 which serves to receive the socket 43 of the lamp bulb 44 which is provided with a two-wire service connection at 45. The lower end of the sleeve 43 is provided with an internal shoulder at 41, upon which a glass diaphragm 46 is seated in pressure-tight relationship. The outer and lower edge of the internal sleeve 33 is provided with a groove at 47 by means of which a thin rubber diaphragm 48 is attached over the end of the sleeve 33 by the retaining band 49. The space between the thin rubber diaphragm 48 and the glass 46 is thus a pressure chamber, into which an inlet tube at 51 extends, the inlet tube being connected to a small pressure tube 50, as shown in Figures 2 and 4. At the lower end of the frame piece there is attached a pad 52 which serves to receive a photoelectric cell unit generally designated 53, the unit being composed of barrier layer photoelectric elements as follows: The edge elements 54-54 are of major area and are responsive to infra-red light, whereas the center elements 55 which has the minor area of the unit is responsive to red light. The light which falls upon the elements 54-54 and 55 is determined by the particular filters situated over them in the cover plate 56.

The infra-red responsive photocell areas 54-54 are covered by two Wratten 88A gelatin filters and the photocell-filter is responsive to light of wave lengths in the range of 720 to 900 millimicrons and has a peak response in the neighborhood of 790 millimicrons. The red light responsive area 55 of the barrier layer photocell is covered by a Wratten 29F filter which transmits light of wave lengths of more than 600 millimicrons, the red cellfilter being responsive to light in the range of 600-900 millimicrons and having a peak response in the neighborhood of 640 millimicrons. Other types of light filters may be used so long as they are capable of transmitting light in the above defined ranges.

Referring to Figure 6 the electrical connection to the earpiece includes the cable generally designated 22 having six conductors, as shown in Figure 6. One pair of conductors 57-57 extends from the positive and negative sides of the infra-red photocells, which are connected in parallel, whereas another pair of conductors 58-58 extends from the red light responsive photocell 55, and pair to the light source 44. The electrical conductors 45-45 to the light source 44 and 5758 to the barrier layer photocell areas of the earpiece are grouped together and are bundled with the small-gauge pressure tubing and with a fine gauge steel supporting wire 60, the whole being joined together by a plurality of small clips 61-61. The fine gauge steel wire is mechanically fastened to the female plug connector 23 at the ferrule 62, as shown in Figure 1, and the fine gauge pressure tubing 50 is taken off to the side and is provided with a convenient pressure connection at 63, all as shown in Figure 1. The steel wire 60 serves to provide mechanical support for the weight of the earpiece and the fine gauge pressure tubing 50 serves to provide a convenient means of applying pressure to the pressure chamber within the earpiece, between the glass and thin rubber diaphragm 46 and 48, respectively, for inflating the rubber diaphragm, as subsequently described herein.

When the device is desired to be used for the analysis of whole blood which is withdrawn from the patient, the earpiece 12 is disconnected at the connection 21-23 of Figure l, and a cuvette apparatus generally desig nated 70, shown in Figures 7-10, is utilized. The cuvette apparatus includes a housing having a bottom plate 71 of plated brass or other sanitary metal. preferably chromium plated. This plate is provided with a central groove at 72 extending almost from end to end of the container, in which there are situated two barrier layer photoelectric elements 73-73, which are responsive to infra-red light, and a central much smaller barrier layer photoelectric element 74 which is responsive to red light. The electrical connections to the unit are carried out through the sub-housing 75 having a screw type connection at 76 which serves to support the terminals which are grouped together at 78. As with the earpiece, one connection is provided to each of the barrier layer photoelectric elements and another pair of connectors is provided for the illumination of the apparatus, as will be described.

The barrier layer photoelectric elements 73-73 and 75 are covered by a filter plate at 77 which has two Wratten filters No. 88A to cover the infra-red responsive portions of the photocell, namely areas 73-73. This Wratten No. 88A gelatin filter is capable of transmitting light in the range above 720 millimicrons. sponsive barrier layer cell 74 is covered by a red Wratten 29F filter, which transmits light of wave lengths greater than 600 millimicrons. As in connection with the earpiece 12 previously described, other specific filters may be r eplaced so long as they transmit light of the wave lengths above specified.

Above the filter plate 71 there is provided a wall section at 79 having an open interior in which there is placed a plurality of spaced plates as follows: The plate 81 is at the bottom of this portion of the apparatus and rests on the filter plate 77, the plate 81 being provided with a central groove 82. The plate 81 is of metal and is provided with a light slit at 83 throughout approximately its entire length. In the groove 82 there is placed a slip of glass 84 which is of the same thickness at the depth of the groove 82 and hence presents a flat upper surface when considered with the plate 81. Above the plate 81 are a pair of spacer elements 85-85 of equal thickness and of a Width such that" when they are positioned as shown in Figure 9, they will permit a small space 0 to exist between them. Above these members 85 is another metal plate 80 which is identical to plate 81. Plate 80 has a slit 86 throughout its entire length along its center line and provided with a space 87 to receive a glass plate 88. When assembled as shown in Figure 9, the glass plates 88 and 84, together with the light impervious plates 85-85, present a central longitudinal opening 0 of uniform thickness from top to bottom and uniform width from side to side, extending entirely throughout the apparatus, it being noted that the wall sections 80 and 81 are provided with apertures at 90-90 in the end walls in alignment with the space thus provided at 0. Through the space and holes thus provided a tube 110 of plastic is inserted. Above the plate 86 is a filter frame 91 into which light diffusing and/ or filter screens 92 can be fitted and above this is provided an insulating block at 89 which is best observed in Figure 8. The insulating block 92 is provided with a recess 93 at its under side and is provided with a plurality of apertures at 94 along its center line immediately over the slight slit 83 and 86. The under side of the plate 92, is covered in the space 93 with a pair of connection sheets, thus sheet 95 of metal which extends from the right end to the center line and another sheet 96 which extends from the left end approximately to the center line, it being noted that the two sheets 95 and 96 are not connected to each other, being separated by the slits 97. The sheets 95 and 96 are held in lace by metal gromlets 98. Above the insulating plate 92 there is a metal plate 104 threaded to receive instrument type electric lamps 99.

Electrical connection is made from one of the terminals 78 of the junction box of the unit to, for example, the plate 95 and from it the circuit extends through the gromlet to the contact area 100 of the lamp 101, whence the circuit continues through the filament of the lamp and to the metal ferrule 102 of the lamp, which is in electrical connection to the plate 85. All of the five lamps to the right of the center line of Figure 8 are in parallel and the current flowing through these lamps is collected in the plate 95 and flows across the plate to the left and thence flows in a downward direction through the screw ferrules of the five lamps at the left end of the center line and through the lamps in parallel and thence through the connection plate 96 to another terminal 78 in the connection block. Thus, the lamps are connected in two groups in series, the lamps in each group being in parallel with each other. In this way a plurality of small instrument lamps can easily be wired for simultaneous illumination and any one of them can be removed for examination or replacement.

It may be noted that the filter frame 91 is mounted so as to slide endways to the right, as shown in Figure 8, so as to permit the filter unit 92 to be withdrawn for change and replacement as desired. The filter units 92 are used to standardize, adjust and check the response of the instrument and are removed from the filter frame 91 during determinations on blood. In the space 0 previously described, there is situated a polythene tube which is supported at the end by gromlets 111-111 held The red rein the brackets 112-112 supported from the housing. The tube is connected to the sanitary stop cock 113 at one end and to a hypodermic needle connection 114 at the opposite end. When the tube 110 is positioned within the instrument it is compressed slightly between the glass plates 88-84, and the side plates 85-85, so that it presents a cross section of thin, fiat, somewhat rectangular shape, as shown in Figure 9. The tube is thus held to a uniform dimension from top to bottom and the whole blood or other fiuid within the tube is thus exposed through the slits 83 and 86 uniformly for a given distance within the instrument.

The electrical connections to the instrument are shown in Figure 10 wherein the terminals 116 of the plug connection are connected through the wires 117 to the studs 118 and 119. The electrical connections from the stud 118 is by means of the wire 120 to the connection plate 95 previously described, thence through the lamps 121 in parallel to the plate 104 and thence through the lamps 122 in parallel to the connection plate 96 and by wire 123 to stud 119. The terminals 124 and 127 are connected by a pair of conductors to the positive and negative terminals of the infra-red responsive photocells 73-73. Similarly, the positive and negative terminals of the red light responsive barrier layer photocell 74 are connected by a pair of conductors 129 to terminals 128 and 130. The entire plug connection 126 is identical with that at 23 and may conveniently be connected to the connection terminal 21, of Figure l where it is desired to replace the earpiece 12 by means of the cuvette 70.

Referring to Figure 11 there is illustrated a wiring diagram of the control cabinet and the earpiece 12 or cuvette 70, and of the galvanometer 11. The upper portion of the wiring diagram, Figure 11, and the central lower portion are all contained in the control cabinet, the earpiece 12 or cuvette 70 being connected to the control cabinet by means of the plug connection 9 into the socket 14 and the galvanometer being connected by means of the plug 19 into the socket 13. The battery leads are connected to the socket 17.

In the control cabinet the switch generally designated 51 is a gang switch having twelve switch arms designated 131-142 inclusive. The switch arms are operated simultaneously by a common mechanical operating shaft 143 and each switch arm is arranged so that it operates over and contacts with five contacts selectively, which are designated off, infra-red, saturation, normal and cuvette-saline. It will be understood that when the switch S1 is moved to any of the positions above designated, for switch 131, the contact arms of the remaining switches 132-142 will be at corresponding angular positions. Thus, in Figure 11 the switch S1 is shown as the saturation" position and all of the contents 131-142, inclusive, are shown in the horizontal position in Figure ll in contact with the middle one of the five arcuately arranged contacts of each switch.

From the battery plug 17 switch leads 149 and 144 are connected through the on-ot'f battery control switch S3 and thence continue as battery positive lead 145 and battery negative lead 146 within the interior of the control cabinet. The leads 145 and 146 are connected directly to terminals 147 and 148 of the galvanorneter receptacle 13 and when the galvanometer plug 19 is plugged into the receptacle 13, contact is established to the lamp 150 of the galvanometer. From terminal 151 on switch S3 a circuit continues via line 152 to junction 153 of a resistor control network, including potentiometer resistors R16 and R17. The resistor R16 has a variable shunt 154 and resistor R17 has a variable shunt 155, the opposite terminals of these resistors being connected to the two terminals 156 and 157 of the switch S2. From terminal 157 line 158 continues through junction 159 to terminal 160 of the voltage-current control switch S4, which determines whether the meter 27 reads voltage or current. The blade of switch S4 is connected by line 161 to one terminal of the meter 27 and the opposite terminal of the meter is connected by line 162 which extends through junction 163 to the terminal 164 on the receptacle 14 of the control cabinet, into which the earpiece or cuvette connection cable 20 is adapted to be connected by means of the multiple prong plug 9. From negative battery supply lead junction 165 a circuit extends through line 166 to one terminal of resistor R19, the opposite terminal of which is connected to terminal 167 of the switch S4. Resistor R18 is connected from junction 163 on line 162 to junction 159 on line 158. The negative battery supply line 146 on the interior of the control cabinet is also connected to terminal 169 on the receptacle 14. When the plug 9 of the earpiece 12 or cuvette 70 is inserted into the receptacle .14, a circuit is established from terminals 164 and 169 to the lamp of the earpiece, which is designated 44, or the plurality of lamps of the cuvette, the lamps in the cuvette being designated 101.

The purpose of switch S4 and resistors R18 and R19 is to permit the use of the meter 27 either for the measurement of current flowing through the lamp or lamps of the earpiece or cuvette, or alternatively to measure the voltage which is applied across the terminals 164 and 169 serving the lamp or lamps. Since it is the current flowing through the lamp or lamps which is determinative of the brilliance of illumination, the current measurement is most readily relied upon, this measurement being taken by moving the switch S4 to contact 160, at which time the meter measures the voltage drop across resistor R18. However, in many installations, where a cable 20-22 of constant length is being used from day to day, a voltage measurement is equally convenient, this being taken by moving the switch S4 to the terminal 167, in which event the meter 27 measures the voltage from terminal 163 to 165, through the resistor R19.

The resistors R16 and R17, switch S2 and the variable shunts 154 and 155 are used for controlling the current through the lamps. The variable shunts 154 and 155 are preferably ganged together and are controlled by the knob 28 on the face of the control panel of the control cabinet 10. By closing the switch S2 and increasing the shunted portion of resistors R16 and R17, the current flowing to the lamp 44 or the lamps 101, may be increased. By turning the knob 28 so as to reduce the shunted portion of resistors R16 and R17, the current may be decreased and by opening the switch S2 the current may be decreased even further.

The coil of galvanometer No. 1 is connected through cord 18 to terminals 170 and 171 of the plug connector 19, while the coil of galvanometer No. 2 is similarly connected to the terminals 172 and 173 of the plug 19, it being understood that both galvanometer coils are in the same instrument and read on the same scale. When the plug 19 is inserted into the receptacle 13, connection is made by terminals 170 and 171 to lines 174 and 175, respectively, of the control cabinet, while terminals 172 and 173 from the coil of galvanometer unit No. 2 are connected to lines 176 and 177.

Line 174 extends through resistor R5 to the blade element of switch 131. Line extends through unction 179 and thence through resistor R7 to junction which is connected to terminal 191 of switch 132. From junction 190 a circuit extends through a resistor R6 to contact 192 of switch 131. From junction 179 line 175 extends also to the movable contact of switch 136.

Line 176 from the coil of galvanometer No. 2 extends through resistor R8 to the movable contact of switch 133. Line 177 from the coil of galvanometer No. 2 extends through junction 193 from which a circuit extends through resistor R10 to junction 194 and to contact 195 of switch 134. From junction 194 a circuit extends through resistor R9 to contact 196 of switch 133. From junction 19% line 177 also extends to the movable contact of switch Referring to the earpiece-cuvette plug and socket connection 9-14 it will be noted that the negative terminal of the red light responsive photocell unit R is connected by one of the lines 58 (or 129 if the cuvette is used) to terminal 197 and that the positive terminal of the red light responsive photocell R is connected by the other line 58 (or 129) to terminal 199. Similarly, from the negative infra-red light responsive photocell IR a circuit extends through line 57 (or 125 if the cuvette is used) to terminal 201 and from the positive terminal of the same photocell a circuit extends through the other line 57 (or 125) tothe terminal 204. When the plug connection 9 is inserted in the socket 14, the terminals 197, 199, 201 and 204 establish contact with, respectively, lines 205, 206, 207 and 208, and the lamp 44 (or 101) are connected to terminals 164 and 169. Line 205 extends to the movable contact of switch 142, whereas line 208 exetnds to the movable contact of switch 141. Line 206 extends to the movable contact 139 and line 207 to the movable contact of switch 140.

Contacts 210, 211, 213 and 214 of switch 131, which are, respectively, the 011, infra-red, saturation and normal switch positions are connected together and are connected through line 215 to the similarly connected together contacts 216, 217, 218 and 219 of switch 132. Similarly, the 011, infra-red, saturation and normal contacts of switches 133 and 134 are all connected together by means of line 220, these contacts being designated .221-224, inclusive, for switch 133 and 225-228, inclusive, for switch 134. The off, infra-red and saturation contacts of switch 138 designated, respectively, contacts 229-231 are connected together by line 232 extending through resistor R12 and thence through line 233 to junction 244 whence line 233 extends to the off contact 234, the infra-red contact 235 and saturation contact 236 of switch 137. From junction 244 line 238 extends to junction 239 and thence to the off contact 240 of switch 136. From junction 239 a line 242 extends through resistor R11 to line 245 and thence to the oil contact 246 of switch 135. From the movable contact of switch 137 a line 248 extends to the movable contact of switch 134. The normal contact 249 of switch 135 and the cuvette-saline contact 250 of the same switch are connected together and are connected through line 251 to terminal 252 of resistor R3 and thence through the resistor to terminal 253 which is connected through resistor R13 to junction 254, whence the circuit extends through line 255 to the cuvette-saline contact 256 and the normal contact 257 of switch 136. Line 255 also extends from junction 254 to the corresponding cuvette-saline contact 258 and normal contact 259 of switch 141. From the sliding contact 261 on resistor R3 line 263 extends to the cuvette saline contact 264 and the normal contact 265 of switch 140. The cuvette-saline contact 268 and normal contact 269 of switch 139 are connected through line 270 to the variable contact 271 of resistor R4, which has its terminal 272 connected through line 273 to resistor R14 and thence through line 274 to junction 275 and to the cuvette-saline contact 276 and the normal contact 277 of switch 138. From junction 275 a branch 280 extends to the cuvette-saline contact 281 and the normal contact 282 of switch 142. The saturation contact 285 and the infra-red contact 286 of switch 142 are connected through line 287 to the saturation contact 288 and infrared contact 289 of switch 141, from which line 290 extends to junction 291 between resistors R1 and R2. The terminal 292 of resistor R1 is connected via line 293 to saturation contact 295 and infra-red contact 306 of switch 136. From the movable contact 299 on resistor R1 line 300 extends to the saturation contact 301 and infra-red contact 302 of switch 140. From junction 291 a circuit extends through resistor R2 to terminal 303 which is connected via line 304 to the saturation contact 298 and the infra-red contact 297 of switch 135. From the movable contact 308 on resistor R2 the circuit extends via line 309 to the saturation contact 310 of switch 139. It may be noted that the off contacts of switches 140-142, inclusive, have no circuits connected to them and that the off and infra-red contacts of switch 139 likewise have no circuits connected to them.

Operation When the instrument is out of service the battery switch S3 is turned to the ofi position, thus de-energizing the lamp 150 of the galvanometers and the lamp or lamps 44 of the earpiece or lamps 101 of the cuvette should the latter be connected. At the same time switch S1 is turned to the off position. In this position a circuit may be traced from the coil of galvanometer No. 1 through terminal 170, line 174, resistor R5, movable contact of switch 131, contact 210 of switch 131, line 215, contact point 216 of switch 131 and through the movable contact of that switch, thence via line 315 to the movable contact of switch 135 and through contact 246, line 245, resistor R11 to contact 240 of switch 136, thence through the movable contact of that switch and through line 175 to the opposite terminal of the coil of galvanometer 1. In this way galvanometer 1 is connected across a total resistance, namely resistances R5 plus R11 in series, which is equal to the critical damping resistance of the galvanometer. The galvanometer thus in the off position is kept in its most serviceable condition. Similarly, when the switch S1 is in the off position, the coil of galvanometer unit 2 is connected across resistors R8 and R12 in series, which likewise equal the critical damping resistance of the coil of galvanometer 2.

To put the instrument in operation switch S3 is turned to the on position. This turns on the light 44 in the earpiece or lights 101 in the cuvette, whichever is connected. The switch S2 is set for the earpiece or cuvette, depending upon which is being used. This switch S2 varies the amount of control obtained by resistors R16 and R17. The switch S4 can be set to either the voltage position, in which the voltmeter measures the voltage across the lamp of the cuvette (or earpiece, whichever is connected), or to the current measurement position in which it measures the current through the lamp or lamps. It is assumed that the galvanometer earpiece (or cuvette) and battery connections are established. The spotlight on the galvanometer should now be illuminated and the mechanical zero of the two galvanometers should be adjusted to zero with the switch S1 in the off position. In this position the switch S1 connects resistors across the galvanometer terminals such that the galvanometer has optimal damping characteristics.

Earpiece operation, switch S1 in normal operation. Double scale operati0n.Double scale operation means separate galvanometers for the red and the infra-red cell outpupt. After the galvanometers have been zeroed, as above described, the switch S1 is moved to normal position. The earpiece is then attached to the ear by adjusting nut 38 so as to loosen the cylinder 33 and bring the uninflated membrane 48 against the ear, clamping it against photocell holder 56 and turn switch S3 on. This illuminates the lamp in the earpiece. Switch S2 should then be set in the earpiece position and the voltage current switch set in the voltage position. Control R16, R17 should be adjusted to appropriate value of voltage, sufficiently low in order not to burn the ear or cause discomfort. Control of R3 and R4 can be adjusted to give appropriate deflection and the galvanometer watched until they have reached equilibrium. Where the galvanometer spots of the red and the infra-red have reached equilibrium, this indicates that the car has been flushed due to the heat of the lamp in the earpiece. The term flushed means that the ear has nearly total arterial blood which flows freely through the loosely held pinna of the ear. During this time the switch S1 should be in the normal position. A simplified diagram of the circuits in this condition of switch S1 is shown in Figure 12 with the switch S1 therein shown at the normal position. After the ear has become flushed and the galvanometer spots have reached equilibrium, pressure is applied to the ear capsule by means of applying pressure through tube 50 to pressure capsule 48 until a pressure of 200 mm. of mercury is obtained. This causes the diaphragm 48 to press against the car with a pressure greater than the blood pressure squeezing the blood from the tissue in the light path between the light 44 and the photocell 5454 and 55. With the blood removed from the tissue adjust the control R3 until the infrared spot on the galvanometer reads divisions and red galvanometer spot reads 100 by adjusting control R4. This is done to facilitate ease of later calculation of the oxygen saturation. The reading on the infra-red galvanometer will be called IRo and the reading on the red galvanometer R0. After the galvanometer has been properly adjusted by controls R3 and R4, the pressure is reduced to atmospheric on the pressure capsule, at which time the infra-red and red galvanometer spots will be reduced to a value below 100 or below what they had been adjusted to in the bloodless ear condition. Readings are now taken of both the red and the infra-red galvanometer deflection at appropriate intervals of time and these readings will be known as on the infra-red IRN and on the red RN.

Therefore, a value which is a function of the absorption of infra-red light by the blood (IRE) can be obtained by the following equation:

IR =log IR 1og IR =log g in which 1R0 is the galvanometer deflection produced by path of the earpiece can be obtained by the expression in which R is the galvanometer deflection produced by the red cell when the ear is rendered bloodless and RN is the galvanometer deflection obtained from the bloodcontaining ear.

The light absorption by blood in the near infra-red is a function of the total amount of hemoglobin contained in this blood. Likewise, the absorption of red light is a function of the amount of oxyhemoglobin and total .hemoglobin contained in this blood. Therefore, the

ratio RB/IRB is a function of the oxygen saturation of the blood interposed in the optical path of the earpiece. Since this blood is rendered arterial by the increase in blood flow through the ear produced by the heat of the earpiece, the expression RB/IRB gives a value which is a function of the percentage saturation of arterial blood with oxygen.

Cuvette operation, switch S1 in cuvette-saline positi0n.This is identical to the operation with the earpiece with the exception that switch S2 is adjusted to the cuvette-saline position, in which case the simplified wiring diagram is as shown in Figure 12 with the switch S1 in the cuvette-saline position therein. Resistors R16 and R17 will also have to be readjusted to appropriate values. The patient is made ready and hypodermic needle, cardiac catheter or other device is inserted in the patient for drawing the blood sample, the cuvette is placed between the needle and the hypodermic syringe with appropriate connections so that saline solution can be flushed through the cuvette. With the cuvette full of saline solution and switch S1 adjusted to cuvettesaline position, adjust controls R3 and R4 until the infra-red and red spots, respectively, indicate 100 on the galvanometer. The designation R0 is given to the red reading of galvanometer No. 2. The designation 1R0 is given to the infra-red reading of galvanometer No. 1. The hypodermic syringe, not shown, which is connected to tube 114 is then manipulated so as to withdraw the saline solution from the tube 110 of the cuvette and to draw blood from the patient into and through the tube 110 of the curvette. The switch S1 is adjusted to the normal position when blood enters the cuvette. The blood sample withdrawn into the syringe may be accumulated for later chemical or other analysis or reinjected into the patient. The readings on the galvanometers are then taken. The reading of galvanometer 1 is designated IRN, and the reading of galvanometer 2 is RN. The readings are then taken with the blood in tube 110. In the cuvette-saline position of switch S1, the sensitivity of the galvanometers 1 and 2 is reduced to one-fourth as much as they are in the normal position due to the resistors inserted in series with them in the curvette-saline position. Accordingly, the R0 and 1R0 readings, which were taken in the cuvette-saline position are both multiplied by four and the values so obtained are used with those obtained in the normal position, viz. the IRN and RN readings, for calculating the percentage oxygen saturation of whole blood in accordance with the method above given. Galvanometer readings may, if desired, also be taken with blood stationary in tube 110 of the cuvette 70 for a period of 30 seconds or more and the oxygen saturation of the blood determined in accordance with the foregoing procedure.

The filter slide 92 is provided for purposes of checking the instrument and several filter media are provided in several slides 92. One filter media is such that its spectral transmission characteristics are approximately the same as for arterial blood of 100% oxygen saturation and another slide includes a filter having spectral transmission characteristics equal to arterial blood of, for example, 20% oxygen saturation. These filters, after having been constructed and calibrated against actual blood analyses and readings corresponding to them, may thereafter be used for purposes of quickly checking the instrument by inserting first one filter and then another into the cuvette and adjusting the instrument accordingly.

Single scale 0pcrati0lz.--Switch S1 in the saturation or infra-red positi0n.In accordance with the present invention the identical instrument may be utilized for making direct in vivo determination of the percentage oxygen saturation of arterial blood or direct readings of the oxygen saturation of blood as drawn through the cuvette apparatus of the invention. For in vivo determinations the instrument is used in accordance with the following method:

1. The switch S3 is moved to the on position and switch S2 is adjusted to the earpiece position. The light source rheostat, viz. R16-R17, is then adjusted to the correct amperage and the voltage and amperage through the light or lights are then checked.

2. The pressure capsule 48 of the earpiece is then inflated to 10 mm. Hg in order to test it for leaks. The earpiece is then adjusted onto a filter designated the T- filter which has approximately the same spectral transmission characteristics as that of a normal ear containing blood of 90% oxygen saturation. With the earpiece thus adjusted the switch S1 is moved to the infrared position and the earpiece and galvanometer are permitted to warm up for at least five minutes.

3. The control switch S1 is then adjusted to the off position and the zero position on the infra-red indicating galvanometer, viz. galvanometer unit 1 is mechanically adjusted so that the indication spot of the galvanometer comes to rest at a predetermined zero position on the scale determined for earpiece 12 (or cuvette 70, if used) by chemical analysis or comparison with known standards. This adjustment is made by means of the usual mechanical adjustment of the galvanometer (not illustrated) by which the galvanometer coil is mechanically changed in position so as to permit the galvanometer indicator spot to come to rest at any position with no current flowing. For example, the galvanometer may be adjusted for a particular earpiece so as to zero at the 96 on the B scale.

4. The foregoing preliminaries having been accomplished, the instrument is then checked against a series of filters as follows:

(a) The earpiece being in place on the T90 filter, the switch S1 is adjusted to the IR position and the infra-red potentiometer resistor R1 is regulated so that galvanometer 1 reads at a predetermined infra-red setting on the B scale (for each earpiece or cuvette), for example 22 on the B scale, as determined by chemical analysis or comparison with known standards.

A simplified diagram of the circuit of the instrument in the infra-red position is shown in Figure 14, in which it will be noted that the red cell is open circuited in respect to its resistor R2, whereas the infra-red cell is connected across a portion of its resistor R1. Hence, in this position the infra-red cell alone provides the potential deflecting galvanometer No. 1.

(b) The switch S1 is then adjusted to the saturation position, the schematic diagram of the circuits of which is shown in Figure 13. In this position the red cell and the infra-red cell are connected across the resistors R1 and R2 which are in potentiometer series arrangement in respect to galvanometer No. 1 and hence the potential of both cells controls the galvanometer deflection, the red cell being in bucking relation to the infra-red cell. In this position the red cell potential deflects the galvanometer reading which was at, for example, 22, up to the previously established Zero position at 96.

(c) The earpiece is then placed on a filter known as the T-BL filter which has approximately the same spectral transmission characteristics as that of a bloodless ear. The red potentiometer resistor R2 is re-adjusted so as to bring the galvanometer reading to the originally predetermined zero position, which was, for example, 96 on the B scale of galvanometer 1.

(d) The third scale is also provided for galvanometer 1 known as the C scale, as shown in Figure 15, and has been previously calibrated by reference to chemical or other analyses or comparison with known standards so as to read directly in percent oxygen saturation. With the T-90 filter again in place on the earpiece and switch S1 in the saturation position, as previously defined, galvanometer 1 should at this time read approximately 90% on the C scale, which is the per cent oxygen saturation represented by the T-90 filter.

(e) A T-20 filter, which has approximately the same spectral transmission characteristics of reduced blood of about 20% oxygen saturation, is then placed on the earpiece and a reading is taken on the C scale which should indicate such percentage. Any number of intermediate percentage points may be established to calibrate the C scale of percent oxygen saturation.

In the following procedure the same adjustments as above described are made with the earpiece in place upon t e ear:

5. The light source switch is turned off and the earpiece is then placed upon the human ear. Attempt is made to position the earpiece so that the flattest portion of the pinna of the ear is interposed in the optical pathway of the earpiece. The inherent strength of the spring 34 of the earpiece alone is permitted to force down the inner cylindrical member 33 upon the pinna of the ear and determine the snugness of the fit, after which the thumb nut 38 is screwed down so as to lock the cylindrical member 33 in place and fix the earpiece in position.

6. The light source of the earpiece is then illuminated and the pressure capsule is inflated to approximately 200 mm. of Hg for a few seconds and then is deflated. This short time inflation and deflation is utilized in order to smooth out any irregularities of the ear which may have been induced by placing the earpiece thereon. Then, with the light source illuminated, the earpiece and car are permitted to Warm up for minutes or more 7. After the warm-up period the switch S1 is adjusted to the IR position and the infra-red potentiometer resistor R1 is adjusted so that the reading of galvanometer 1 is at the predetermined infra-red setting, which was, for example, 22 on the B scale of that galvanometer. The galvanometer reading with the control switch S1 in the off position should remain at the predetermined zero position, which was, for example, 96 on the B scale of galvanometer 1, all adjustments having been properly made.

8. The switch S1 is then adjusted to the saturation position and the pressure capsule 48 is inflated to a pressure of 200 mm. of Hg or more for a period of 30 seconds. After pressure has been applied for about seconds the red potentiometer resistor R2 is adjusted so that the galvanometer comes to rest at the zero position on the B scale of galvanometer 1. Pressure can be released after adjustment has been attained. This adjustment should be completed as nearly as possible at the completion of a second period of application of pressure to the ear.

9. The galvanometer reading is now taken and indicates the percent oxygen saturation of blood directly on the C scale of galvanometer 1.

10. The galvanometer reading with switch S1 adjusted to the IR position should be recorded at intervals. If this value changes appreciably adjustments described in paragraphs 7 and 8 should be repeated. The reading taken in the IR position is almost independent of the oxygen saturation of the blood and is proportional to the total blood and tissue in the optical path.

11. In any case at the end of the procedure the ear capsule should be inflated to 200 mm. of: Hg for 30 seconds and the readings on the B scale of galvanometer 1 should be recorded at 30 seconds with the control switch in the saturation position. This reading corresponds to that described in paragraph 8 and is for checking purposes.

Where single scale operation is carried out using the cuvette, the infra-red setting of paragraph 7, is made with blood in the tube 110 cuvette 70 stationary for a period of 30 seconds, switch S1 in the IR position. The zero position setting is then made with the tube 110 filled with saline solution and the switch S1 in the saturation position.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiment herein.

What I claim is:

1. A galvanometer having a coil and scale, said coil having a range of operable deflections on said scale, a photoelectric cell and light filter therefor, designated the infra-red cell, responsive to light in the range of 720 to 900 millimicrons and having a peak response at approximately 790 millimicrons, another photoelectric cell and light filter therefor, designated the red cell, responsive to light in the region of 600-900 millimicrons and having a peak response at approximately 640 millimicrons, means for illuminating the photocells with light passed through tissue containing blood and for excluding the blood from the tissue while the light is passed therethrough, said galvanometer being mechanically adjusted so that it is undeflected at a position intermediate the ends of its operable range of deflections when no potential is applied thereto, means for selecting a proportion of the voltage of said infra-red cell, means for selecting a proportion of the voltage of the red cell, means for connecting only the selected portion of the voltage of the infra-red cell to said galvanometer and for connecting the selected portions of said infra-red and red cells to said galvanometer in bucking relationship, said galvanometer having a sensitivity such that when the infra-red cell is illuminated by light passing through tissue containing blood, the coil of the galvanometer will be deflected appreciably from said mechanically adjusted undeflected position by said selected proportion of the voltage of the infra-red cell, and when both cells are so illuminted by light passing through tissue from which blood is excluded and the selected portion of the red cell potential is connected in bucking relation to the previously selected portion potential of the infra-red cell, the galvanometer will be returned towards said mechanically adjusted position, said scale having a calibrated portion for indicating percentage oxygen saturation of blood when light is passed through tissue containing blood and said light falls on said photocells simultaneously.

2. The apparatus of claim 1 further characterized in that the undeflected position to which the galvanometer is adjusted is within the limits of the calibrated portion of said scale indicating oxygen saturation.

3. The apparatus of claim 1 further characterized in that the sensitivity of the galvanometer, per se, is such that it is deflected appreciably beyond the calibrated portion of said scale when the potential of either the red or the infra-red cell alone is applied to the galvanometer and light illuminating said cell is passed through tissue from which blood is excluded.

4. An apparatus for determining the absolute percentage oxygen concentration of blood comprising a galvanometer having a coil and a scale, said coil having a range of operable deflections on said scale, a photoelectric cell and light filter therefor designated the infrared cell, responsive to light in the range of 720 to 900 millimicrons and having a peak response at approximately 790 millimicrons, another photoelectric cell and light filter therefor designated the red cell, responsive to light in the range of 600 to 900 millimicrons and having a peak response at approximately 640 millimicrons, light source means for projecting light along an optical pathway and through said filters and onto said photocells simultaneously, means for holding blood in vivo in said optical pathway in a position such that light is projected therethrough, additional means for excluding blood from said optical pathway while the projection of light along said optical pathway and onto said photocells is continued, said galvanometer being mechanically adjusted so that it is undeflected at a position intermediate the ends of its operable range of deflection when no potential is applied thereto, means for selecting a proportion of the voltage of said infra-red cell, means for selecting a proportion of the voltage of the red cell, means for connecting only the selected portion of the voltage of the infra-red cell to said galvanometer and for connecting the selected portion of the voltage of said infra-red cell and red cell to said galvanometer in bucking relationship, said galvanometer having a sensitivity such that when the infrared cell is illuminated by light passing through said means for holding blood in vivo while blood is contained therein, the coil of the galvanometer will be deflected appreciably from said mechanically adjusted undeflected position by said selected proportion of the voltage of the infra-red cell, and when both cells are illuminated by light passing through said means for holding blood in vivo while blood is therein, and the selected portion of the voltage ofthe red cell is connected in bucking relation to the previously selected portion of the voltage of the infra-red cell, the galvanometer will be returned toward said mechanically adjusted position, said scale having a calibrated portion for indicating absolute percentage oxygen saturation of blood when light is passed through said means for holding blood in vivo while blood is therein and said light falls on said photocells simultaneously.

5. A device for obtaining in vivo the spectral transmission of blood and tissue and of the tissue when blood is substantially excluded therefrom comprising a frame having supported thereon photo responsive means including a light receiving mechanical support surface, light source means on the frame for projecting a beam of light toward said surface so as to be received thereon, means mounted on the frame for movement toward and away from said surface for lightly holding tissue in vivo mechanically between said means and said surface in a position that light will pass through said tissue in vivo and be received on said surface, means on said frame for compressing said tissue while it is thus mechanically held so that blood is substantially excluded from said tissue while light is passed therethrough onto said surface, said photo responsive means being located so as to be activated by light passing through the tissue and received on said surface.

6. The apparatus of claim further characterized in that said surface is transparent and said photo responsive means is mounted under said surface in a position to receive light projected onto and through said surface.

7. A device for obtaining in vivo the spectral transmission of blood and tissue and of the tissue when blood is substantially excluded therefrom comprising a frame having mounted thereon a light receiving mechanical support surface, photo responsive means connected to the frame for receiving light impinging on said surface; a tube mounted on said frame with its axis generally normal to said surface, said tube being mounted for movement of the end of the tube toward and away from said surface for lightly holding tissue in vivo between the end of the tube and said surface, a fluid pressure expansible light transmitting wall mounted on the frame between the tube end and said surface, said wall being movable toward the surface when pressure is applied for compressing tissue in vivo against the surface for substantially excluding blood from said tissue, and light means on the frame for projecting a light in a generally axial direction through the tube and light transmitting wall and onto said surface.

8. The apparatus of claim 7 further characterized in that said fluid pressure expansible light transmitting wall is attached across that end of the tube which is most adjacent the surface, and that portion of the tube adjacent said wall is made pressure tight and is provided with a pressure connection.

9. A device for obtaining in vivo the spectral transmission of blood and tissue and of the tissue when blood is substantially excluded therefrom comprising a frame having mounted thereon a light receiving mechanical support surface, photo responsive means connected to the frame for receiving light impinging on said surface, a generally tubular member mounted on the framesfor movement in a generally axial direction for bringing the end of the tubular member toward or away from said surface, spring means on the frame for biasing the movable tubular member towards the surface for lightly holding tissue in vivo between the end of the tubular member and said surface, means for immobilizing the tubular member with reference to said surface, an expansible diaphragm of light transmissible material across the end of the tubular member which is adjacent said surface, at least that portion of the tubular member which is adjacent said diaphragm being pressure tight and having a pressure connection thereto, and light source means on the frame for projecting light generally axially through said tubular member and through said diaphragm and onto said surface.

10. A device for obtaining an absolute percentage value of oxygen saturation of blood in vivo comprising a frame having a platform thereon, a light source on the frame for projecting light along an optical pathway and onto said platform, means for holding a member containing blood in vivo in said optical pathway in a position such that said light is projected therethrough, additional means for excluding blood in vivo from said member in said optical pathway while light is projected through the member and onto said platform, infra-red light responsive photocell means mounted on said frame, red light responsive photocell means mounted on said frame, said photocell means being responsive to light projected into said platform for converting the light transmitted through said sample into separate electrical signals, and indicator means connected to said photocells and responsive thereto.

11. The apparatus of claim 10 further characterized in that said indicator means includes separate indicators connected to and responsive respectively to said infrared and red responsive photocell means.

12. The apparatus of claim 10 further characterized in that indicator means is responsive simultaneously to the electrical signals of said infra-red responsive and red responsive photocell means.

13. An apparatus for determining the absolute oxygen percentage concentration of blood in vivo comprising a galvanometer having a coil and a scale, said coil having a range of operable deflections on said scale, light source means for projecting light along an optical pathway, infra-red light responsive photocell means, red light responsive photocell means, said infra-red light and red light responsive photocell means being mounted so that light projected along said optical pathway is projected onto both of said photocell means, means for holding a member containing blood in vivo in said optical path way in a position such that light is projected therethrough, and additional means for excluding blood therefrom while the light continues to pass along said optical pathway, first voltage proportioning means connected to the infra-red light responsive photocell means for selecting a proportion of the voltage of said photocell means, second voltage proportioning means connected to the red light responsive photocell means for selecting a proportion of the voltage of said photocell connection means connecting said first and second voltage proportioning means and said galvanometer for selectively applying only the selected portion of the voltage of the infrared light responsive photocell means to said galvanometer and for applying the selected portions of the voltages of said infra-red and red cell light responsive photocell means in series bucking relationship to said galvanometer.

References Cited in the file of this patent UNITED STATES PATENTS 2,203,036 Van Briessen et al. June 4, 1940 2,308,095 Meeder Jan. 12, 1943 2,356,238 Gillett et al Aug. 22, 1944 2,358,992 Millikan Sept. 26, 1944 2,423,855 Smaller July 15, 1947 2,436,104 Fisher et al Feb. 17, 1948 2,439,857 Millikan Apr. 20, 1948 2,442,462 Kirschbaurn June 1, 1948 2,498,506 Ramser Feb. 21, 1950 FOREIGN PATENTS 815,244 France July 8, 1937 515,310 Great Britain Dec. 1, 1939 

5. A DEVICE FOR OBTAINING IN VIVO THE SPECTRAL TRANSMISSION OF BLOOD AND TISSUE AND OF THE TISSUE WHEN BLOOD IS SUBSTANTIALLY EXCLUDED THEREFROM COMPRISING A FRAME HAVING SUPPORTED THEREON PHOTO RESPONSIVE MEANS INCLUDING A LIGHT RECEIVING MECHANICAL SUPPORT SURFACE LIGHT SOURCE MEANS ON THE FRAME FOR PROJECTING A BEAM OF LIGHT TOWARD SAID SURFACE SO AS TO BE RECEIVED THEREON, MEANS MOUNTED ON THE FRAME FOR MOVEMENT TOWARD AND AWAY FROM SAID SURFACE FOR LIGHTLY HOLDING TISSUE IN VIVO MECHANICALLY BETWEEN SAID MEANS AND SAID SURFACE IN A POSITION THAT LIGHT WILL PASS THROUGH SAID TISSUE IN VIVO AND BE RECEIVED ON SAID SUFACE, MEANS ON SAID FRAME FOR COMPRESSING SAID TISSUE WHILE IT IS THUS MECHANICALLY HELD SO THAT BLOOD IS SUBSTANTIALLY EXCLUDED FROM SAID TISSUE WHILE LIGHT IS PASSED THERETHROUGH ONTO SAID SURFACE, SAID PHOTO RESPONSIVE MEANS BEING LOCATED SO AS TO BE ACTIVATED BY LIGHT PASSING THROUGH THE TISSUE AND RECEIVED ON SAID SURFACE. 